1. Technical Field
This invention generally relates to electrical heaters and, more particularly, to an apparatus for heating the air/fuel mixture entering the cylinder of an internal combustion engine.
2. Discussion
The prior art has addressed the desirability of heating the environment of the intake manifold including the air/fuel mixture exiting the carburetor of an internal combustion engine in order to increase fuel economy and decrease pollutant discharge. One type of intake heating device generally includes a pair of gaskets surrounding a heating coil or grid disposed between the carburetor and the air intake manifold as shown in U.S. Pat. No. 4,020,812 to Hayward and U.S. Pat. No. 4,106,454 to Henlis. The gaskets in these devices not only prevent air leaks into and out of the manifold but also thermally and electrically isolate the grid from the intake structure. However, as recognized and addressed in U.S. Pat. No. 5,595,164, entitled "Low Profile Intake Manifold Heater", issued Jan. 21, 1997, gasket wear or aging may eventually short the electric circuit through the heating element.
The invention disclosed in U.S. Pat. No. 5,595,164 minimizes concerns relating to shorting of the heating element circuit by recessing at least one continuous coil type heating element in a mounting frame. The heating element is coupled to insulating material that thermally and electrically isolates the heating element from the mounting frame. Additionally, the heating element is shaped to nest within the insulating material which, in turn, floats within a mounting channel formed in the frame. As a result of this floating arrangement, the mounting channel and insulating material cooperate to structurally support the heating element.
While the invention disclosed in U.S. Pat. No. 5,595,164 has performed satisfactorily, still further improvements can be made, especially where engine designs permit them. For example, the cost of insulating material possessing a structural strength sufficient to support the coils, such as a ceramic, is generally greater than the cost of insulated material having less structural integrity. In light of these issues, it is desirable to provide a heating element that rigidly connects a plurality of heating ribbons to a frame or mounting member such that the mounting apparatus exhibits sufficient structural strength to resist the vibrational stresses created by the engine while isolating the electrical connection from the gaskets of the heating device.
A further deficiency present in some of the heater devices is that the heating grids used therein generally consist of a single continuous coil of resistance wire or ribbon having one end connected to an electric power source and a second end connected to ground. While such continuous coils of resistance ribbon may effectively heat the intake air/fuel mixture in the specific applications for which the coils are designed, continuous coils provide only a single heating capacity for a given supply voltage. Thus, if a different heating capacity is desired in a given application, the entire heating coil must often be replaced with a new element having the appropriate resistance or, alternatively, the supply voltage may be changed. The present invention provides a heating element wherein the heating capacity of the resistance ribbon may be varied by adjusting the length of resistance ribbon in the circuit or changing the circuit from a plurality of ribbon elements electrically connected in series to a plurality of ribbon elements connected in parallel.
Finally, heating devices that address some of the above deficiencies include numerous parts for coupling the heating ribbons to the frame or mounting member in a horizontally oriented arrangement that is restrictive of the airflow passing the heating ribbons and into the cylinders.